Electroluminescent devices comprise electroluminescent material that is capable of emitting light when a current is passed through it. The material used for electroluminescent devices can be light emitting polymers or small organic molecules. Organic devices may, for example be organic light emitting diodes (OLEDs), which are known in the art. For activating the electroluminescent devices, current is applied to the electroluminescent material by means of electrodes.
Electroluminescent devices, such as OLEDs, comprise electroluminescent material disposed between electrodes. Upon application of a suitable voltage, current flows through the electroluminescent material from anode to cathode. Light is produced by radiative recombination of holes and electrons inside the electroluminescent material.
Electroluminescent devices using organic electroluminescent material for general illumination have a forward voltage in the range of 2 to 5 Volts. This low voltage makes it unsuitable for direct mains driving. One solution of this problem is to connect as many OLED devices in series as it is required to achieve the required resistance of the electronic circuit. The problems with such kind of circuit are that the OLED peak current is much higher than the average value, the mains current harmonics might exceed regulation limits and the OLED average and peak current values vary greatly with the mains voltage variation.
Another possible solution is an electrical circuitry known as a ballast that is required to operate the OLED devices directly from mains. A ballast converts the AC voltage of the public power grid to a form which is suitable to drive an OLED light source at a prescribed brightness. Proposals to drive OLEDs directly from mains are known from prior art. These solutions are still too expensive to implement because additional circuit elements are required and extra effort for heat management is required. This is primarily due to the lumped element nature of the prior art solutions.
The invention therefore aims to provide an improved electroluminescent device, especially an improved OLED device.